Inerting a volume refers to the procedure of adding low-activity (inert) gases or vapors in atmospheric oxygen, or expelling and replacing ignitable gas mixtures from a closed volume in order to create a low-activity environment in a volume, for example to avert the danger of explosion or fire. For example, fire prevention could be accomplished by expelling atmospheric oxygen out of the volume by means of noble gases, such as argon or nitrogen, or carbon dioxide, thereby averting an explosive atmosphere.
A variety of different systems and methods exist for use in commercial aircraft. For example, inerting systems are known in which an air separation module is used to divide air, e.g. from an aircraft cabin, into an oxygen-enriched and an oxygen-depleted volume flow, wherein the oxygen-depleted share is introduced of the free volume of the aircraft fuel tank. This oxygen-depleted volume flow exhibits primarily nitrogen, and expels the atmospheric oxygen necessary to form an explosive mixture out of the free gas volume into the fuel tank. Further known is the use of ignition spark weakening means (so-called “ignition mitigation means”, IMM), which are used in the form of a polyurethane foam, a foam rubber or the like in fuel tanks of some military aircraft, e.g., the USAF F-15 Eagle and Navy F/A 18 Hornet to prevent explosions. However, the approximately 10-20% reduction in fuel volume might be problematical here, along with maintenance, which encompasses the removal of foam at each tank opening, the storage of contaminated foam, as well as health, safety and environmental aspects. In addition, the fuel tank volume must be recalibrated, and the additional weight of the foam must be taken into account. Consideration must also be given to the fact that the use of foam has not been approved for civilian aircraft.
Also conceivable is the use of nitrogen for introduction into a free volume of a fuel tank, wherein the nitrogen could be entrained in the form of several gas bottles, although the latter would have to be routinely replaced or refilled, and also increase the weight of the aircraft at the same time. There is always a potential risk of explosion associated with the installation of pressurized gas bottles in a vehicle as well.
In view of the properties of the systems and methods known in the art for inerting a gas volume in a vehicle, there may be a need for a new type of system and method for inerting a volume that has both a mechanically simple design and low weight, and is largely maintenance-free. At the same time, there may be a need for the kind of inerting system that requires no replacement or refilling of fuel, while at the same time also not posing any risk to aircraft safety. In addition, other needs, desirable features and characteristics will become apparent from the subsequent summary and detailed description, and the appended claims, taken in conjunction with the accompanying drawings and this background.